Surface treated steel sheet suitable for forming



A ril 14, 1970 H MU UCHIDA ETAL 3,506,413

SURFACE TREATED STEEL SHEET SUITABLE FOR FORMING Filed Oct. 2, 1967 3 Sheets-Sheet l Q 5 0.3 E (U E E U 2 c x (D o '8 x .z x x x X o 1- i l .2 *2 2 0 l I I l 1 Temperature C IN VENToRs HIROMU UdH/Dfl Tosmo HE-Rm nsnYUm mmsucm HIDSHl .SnTo

SURFACE TREATED STEEL SHEET SUITABLE FOR FORMING FIG.2

3 Sheets-Sheet 2 Filed 001;. 2, 1967 IX. X

1 15 Testpiece Number Testpiece Number April 1970 HIROMU UCHIDA ET AL 3,506,413

SURFACE TREATED STEEL SHEET SUITABLE FOR FORMING Filed Oct. 2, 1967 3 Sheets-Sheet 3 Number Testpiece AEEvo3m comcutm Number Tesfpiece United States Patent US. Cl. 29-195 7 Claims ABSTRACT OF THE DISCLOSURE Surface treated steel sheet suitable for forming which comprises a steel sheet having a metallic coating of zinc, lead, azinc base alloy or a lead base alloy thereon, and a layer of a higher carboxylic acid or a higher carboxylic acid containing an amine coated on to said metallic coating. The coatings provide lubricity for forming operations, act as rust inhibitors and have advantageous properties as compared to oils or metallic soap based lubricants previously used on steel sheets in forming operations.

The present invention relates to a surface treated steel sheet suitable for forming. The surface treated steel sheet of this invention is obtained by coating a steel sheet with zinc, lead, zinc based alloy or lead based alloy (hereinafter called zinc or lead), and applying on the coated surface a layer of matter, solid at room temperatures, which comprises a higher carboxylic acid or a mixture thereof with a suitable amount of amine.

Lubricants are generally required when a steel sheet is subjected to a forming operation such as press forming. For this purpose oily products have been used. Recently attempts have been made to use metallic soap based lubricants as substitutes for the oil lubricants. The metallic soap based lubricants have excellent lubricating ability as compared with the oil lubricants. Also, the steel sheet which is coated with such soap bases is easy to handle, since the coating layer is solid and not sticky and thus it can be advantageously used as a coating material for a pre-lubricated steel sheet. On the other hand, the metallic soap based lubricants have disadvantages. A lengthy, high temperature heating period is required to dry such soap based lubricants because they are applied on the steel sheet in the form of an aqueous solution. This leads to decreased productivity and accelerates ageing of the steel sheet substrate thus deteriorating the quality and forming properties of the steel sheet.

The present inventors conducted various extensive experiments and studies in efforts to overcome the above difiiculties with the metallic soap based lubricants. It has now been found that a surface treated steel sheet obtained by applying a metallic coating of zinc or lead, on a steel sheet surface and then applying on the metallic coating a layer consisting of a higher carboxylic acid or a mixture thereof with a suitable amount of amine, wherein said acid or mixture with amine is solid at room temperatures, gives as good a lubricity as that obtained by using the metallic soap based lubricants, and efi'ectuates higher productivity without deteriorating the material quality of the steel sheet, and thus provides a very suitable form of prelubricated steel sheet.

These effects can be attributed to a number of reasons. The metallic surface of zinc, or lead present on the steel surface has a strong affinity with the higher carboxylic acid or its mixture with a suitable amount of amine (hereinafter called higher carboxylic acid based coating material). A thin layer of metallic-soap-like substance is formed 3,506,413 Patented Apr. 14, 1970 "ice by reaction of the metallic coating with the higher carboxylic acid based coating material at the interface therebetween. The metallic-soap-like substance having a higher carboxylic acid radical is regularly oriented in respect to the steel sheet substrate and strongly bonded with the layer on the steel sheet substrate according to its formation history, thus giving a remarkable lubricating eifect.

The experimental results obtained in support of the above conclusion are shown in FIG. 1. FIG. 1 shows the results of measurement of kinetic friction coeificient in a bath of stearic acid obtained with Sodas type II penduram style tester, between a non-plated steel ball and three kinds of pins (1), (2) and (3). Pin 1 is a non-plated steel pin. Pin 2 is a steel pin which is coated with 10 g./m. of zinc by electroplating and pin 3 is a steel pin which is coated with g./m. of lead-tin alloy (Sn: 20 wt. percent) by hot dipping. In the case of measurements below the melting point of the stearic acid, molten stearic acid was coated on the pin by hot dipping. This coated pin was used and the measurements taken in a water bath. The stearic acid used in the test contained a small amount of palmitic acid and had a melting point of 57 C. The zinc stearate corresponding to this stearic acid has a melting point of above 100 C. A metallic soap composed mainly of lead stearate also shows a melting point above 100 C. It should be noted from FIG. 1 that in both the zinc plated pin and the lead-zinc alloy plated pin, the kinetic friction coelficient tends to lower even above the melting point of the stearic acid and shows the minimum point at a temperature above 100 C. This is attributed to the fact that the formation reaction of zinc base or lead base metallic soap proceeds as the temperature increases so that the thus formed zinc stearate or lead stearate in the solid state gives boundary lubricating effects even beyond the melting point of the stearic acid.

On the other hand, in the case of the non-plated steel pin, the minimum point of kinetic friction coeflicient appears at the melting point of stearic acid, and the friction coefficient increases as the temperature increases beyond the melting point. From this it can be seen that the formation of iron based metallic soap does not easily progress even with increases in temperature. Further, the kinetic friction coefiicient near room temperatures shows a lower value in case of the zinc plated pin or the lead-tin alloy played pin.

The above results indicate that when stearic acid is coated on zinc plated or lead plated steel sheet, a thin layer of substance analogous to zinc stearate metallic soap or lead stearate metallic soap is also formed at the interface between the stearic acid layer and the metallic layer of zinc or lead.

Thus it can be concluded that the excellent lubricity of the present steel sheet is based on the presence of a thin layer of metallic-soap-like substance formed on the interface between the metallic coating of zinc or lead and the higher carboxylic acid based coating material. It should be noted that the excellent lubricity can be maintained under most severe forming conditions, such as those encountered in press forming works. This maintenance of excellent lubricity under severe forming conditions is considered to be based on the fact that in the present steel sheet, both the metallic coating and the higher carboxylic acid coating react only partially, and for the most part remain unreacted on the steel sheet surface. Then, when the sheet is subjected to a press forming, the unreacted metallic coating and higher carboxylic acid react with each other to form an additional metallic-soap-like substance even when the aforesaid layer of metallic-soap-like substance is damaged by contact with the press forming tool and is thinned due to the dimensional increase of the steel sheet.

However, the above effects can be obtained only when the layer of higher carboxylic acid based coating is in the solid form at the ordinary temperatures. In case of a similar layer which is in the liquid form at the ordinary temperatures, the coating layer at portions on which heavy load is put during a severe forming work, namely at portions which require lubricant most, i squeezed out thus causing shortness of lubricant and a desirable maintenance of excellent lubricity as above cannot be obtained. For this reason, the layer of higher carboxylic acid based coating is limited to a solid form in the present invention.

The objects and advantages of the present invention will be fully understood through the following more detailed description of the present invention referring to the attached drawings, in which: I

FIG. 1 is a graph showing the relation between tem pertures and kinetic friction coefficient of a non-plated steel pin, an electrolytic zinc plated steel pin and a hotdip lead-tin alloy (tin: 20 wt. percent) plated steel pin respectively with a non-plated steel ball in stearic acid; and FIGS. 25 are graphs respectively showing results of Fukuis Conical Cup Test and Ericksen Test in the examples of the present invention.

The inventive construction of the present steel sheet will be described in more detail.

As the metallic coatings applied on the steel sheet, zinc coating, lead coating or alloy coatings composed mainly of zinc or lead applied by an ordinary electrolytic platings or by an ordinary hot-dip plating are useful. Further the metal coatings applied by the above method may be subjected to thermal treatment to allow the coating metal to diffuse into the steel sheet substrate and convert the surface of the steel sheet substrate to an alloy system containing iron. This also gives eflective metal coatings.

Furthermore, a thin layer of hydrated metal oxide, such as hydrated chromium oxide and/or silicon oxide, may be applied on the above metal coatings by a chemical treatment and the like for the purpose of improving paint adherence or preventing rust formation with almost no deteriorating effects on the forming quality of the present steel sheet.

The coating material, which is solid at room temperatures, for application on the steel sheet according to the present invention, is prepared by selecting higher carboxlic acids and adjusting the amount of amine to be added to the higher carboxylic acids as described hereinafter.

The term higher carboxylic acid used in the present invention means any carboxylic acid having eight or more carbon atoms, which includes, for example, saturated fatty acids having no fewer carbon atoms than that in capyrlic acid; corresponding unsaturated fatty acids; hydroxy carboxylic acids; naphthenic acids; dicarboxylic acids; and natural products composed mainly of the above acids, such as animal oil fatty acids, hardened animal oil fatty acids, vegetable oil fatty acids, hardened vegetable oil fatty acids, petroleum acids etc. Among these, the following are representative acids which are solid at room temperatures: capyrlic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignaceric acid, cerotic acid, montanic acid, melissic acid, elaidic acid, erucic acid, 12-hydroxy stearic acid, suberic acid, sebacic acid, hexadecane-dicarboxylic acid, naphthenic acid, tallow fatty acid, hardened fish oil fatty acid,

'hairdened castor oil fatty acid, petroleum acid, etc.

As amines to be added to the above higher carboxylic acids, there are, for example, primary mono-amines such as lauryl amine and cyclohexyl amine; secondary monoamines such as di-iso-propyl amine and di-cyclohexyl amine; tertiary monoamines such as triethyl amine; polyamines such as di-amino-propane; and oxazines and imid azoles.

These amines are added to the higher carboxylic acids which are solid at room temperatures as mentioned before. However, most of these amines are liquid at room temperatures, and if these amines are added in an excessive amount, the resulting coating material will not be solid at room temperatures. Therefore it is necessary to limit the amount of amine to such amount as to maintain the coating material in the solid state at room temperatures. In most cases this requirement is atisfied by adding the amine in an amount not greater than its chernical equivalent weight to the higher carboxylic acid.

As for the method for applying the above higher carboxylic acid based coating material on the steel sheet coated with zinc or lead, the material may be heated or dissolved in an organic solvent to liquidize it and then applied on the sheet surface by roll coating, spray coating, brush coating, mop coating, dip coating, flow coating, etc. Alternatively, the solid material may be directly spread on the steel surface and then refiowed by heating with an infra-red beam, hot air, etc.

Although the primary purpose of the metallic coating is that of a reaction medium for forming the metallicsoap-like substance, it also acts as a rust preventing coating. Further, it produces uniform coatings by its aflinity to the higher carboxylic acid based coating material.

Zinc or lead metallic coatings of various thickness were applied on steel sheet substrates and the higher carboxylic acid diluted in a solvent was applied thereon. The results showed that in case of the non-alloyed zinc or lead coatings, a uniform coating of the higher carboxylic acid based coating material is obtained when the zinc or lead coating is not less than 250 mg./m. When zinc or lead alloy coatings were used, a uniform coating of the coating material was obtained when the total content of lead or zinc in the alloy was not less than 250 mg./m. An excellent forming character is obtained in these ranges.

As the amount of the metal coating is increased beyond the above mentioned quantities, the higher carboxylic acid based coating material reacts more easily with the metallic coating. It has been found that the lubricating effect by the higher carboxylic acid coating will be improved until the amount of the metallic coating or the the total metal content increases to 2500 mg./m. However, the surface lubricating effect does not decrease and remains almost constant even when the amount of the metallic coating exceeds 2500 mg./m. Therefore any amount of not less than 250 mg./m. of the metallic coatmay be used. As for the rust preventing effect by the metallic coating, a better result can, of course, be obtained by a thicker coating.

A very small amount of the higher carboxylic acid based coating material which is solid at room temperatures is effective. Remarkable effects can be obtained when the coating material is used in an amount greater than 10 mg./m. Although the lubricating effect increases as the amount of this coating material increases, the practical upper limit of the coating material is 5 g./m. in view of possible adherence and accumulation of the coating material on the sheet feeder or forming tools, and re-adherence of the accumulated coating material on the steel sheet, time required for removing the coating material at the last stage, and the necessity to minimize the contamination of the removing liquid.

It has been found that the following effects are obtained by adding an amine to the higher carboxylic acid, as compared to the higher carboxylic acid without addition of amine.

(1) Solubility in an organic solution is increased, and viscosity of the heated molten coating material is easily controlled in the coating operation.

(2) Aflinity with the steel sheet substrate of the coating material is increased and the rust preventing effect is increased.

(3) Washing removability of the coating material by an alkaline base degreaser or an organic solvent is improved. However, an amine having excessive carbon atoms and low aflinity to water, such as myristyl amine, is not desirable for this particular purpose due to its low solubility in an alkaline degreaser.

Naturally, the present invention includes not only a steel sheet both sides of which are surface treated but also a steel sheet wherein only one side is surface treated and further a steel sheet wherein only a part thereof is surface treated. The latter sheets are at times suitable to certain types of forming operations.

The present steel sheets are produced in three steps; production of steel shet substrate (non-plated), coating of metal; and application of the higher carboxylic acid based coating material. However, it is not necessary to conduct the above three steps in the same shop. Each of the steps can be done in a separate shop. The last step of applying the higher carboxylic acid based coating material may be done on the blanking line or just before the forming operation.

Any steel sheet or any steel sheet piece thus produced falls within the scope of the present invention.

Addition of colouring matter, filler or rust preventing additive in the higher carboxylic acid based coating material in an amount insufficient to change the basic nature of the coating material does not damage the specific functions of the present steel sheet.

Various advantageous properties of the present steel sheet are set forth below.

(1) Excellent formability is obtained. This is due to the excellent lubricity of the surface, and thus application of additional lubricating oil is not necessary. For this reason, the efficiency of the forming operation is remarkably improved.

(2) Since the higher carboxylic acid base material is solid, dry and not too sticky, dust does not deposit on the surface and surface defects occur far less often during the press forming. In addition to the fact that only a small amount of the coating material is required, no irregularities, no squeeze-out of the coating material and no transfer of the coating material from surface to surface is seen even when the steel sheets are piled. Therefore it is easy to control and maintain the amount of the coating material to be applied on each side of the steel sheet.

(3) Good weldability is obtained since the coated surface is dry and the higher carboxylic acid based coating material acts as fluxing agent.

(4) The higher carboxylic acid based coating material can be easily removed by an alkaline degreaser or an organic solvent. Contamination by the coating material, particularly, of the alkaline degreaser, is negligible due to the nature of the coating material and the fact that the coating material is applied in a small amount. Also, the zinc and lead based metallic coatings may be, if necessary, removed by an acid solution, such as sulphuric acid, acetic acid, hydrochloric acid, or by a strong alkaline solution. Also, if desired, only the higher carboxylic acid based coating material can be removed after the forming work and the metallic coating can be utilized as a protective and decorative layer for the final product or as a paint coating base or a base for a chemical treatment (such as chromate treatment and phosphate treatment).

(5) In the present steel sheet, if the higher carboxylic acid based coating material is removed after a forming operation and further if the zinc base metallic coating is finally removed by acid pickling, the zinc base metallic coating dissolves acting as a sacrificing anode to the steel sheet substrate during the acid pickling. The finally exposed, naked surface of the steel sheet has very high activity just as in case of cathodic acid pickling and provides an excellent base for permanent plating. When the present steel sheet is used in such applications, a thinner zinc base coating (zinc content in the coating is 250- 2500 mg./m. is advantageous in view of economy and its easier removal. Such a metallic coating is also useful as a pre-coating for promoting a phosphate treatment applied on the steel sheet as paint base etc. and for uniformly forming such a phosphate coating.

(6) Since coating material which does not dry easily, such as a metalic soap lubricant is avoided, a long period of heating is not necessary. This results in higher productivity and avoids deterioration of the quality of the steel sheet substrate.

EXAMPLE 1 Various metallic coatings and higher carboxylic acid based coating material and comparison lubricating oil as defined in Table l were applied on a cold rolled, remined steel sheet of 0.8 mm. thickness, and results of press formability tests are shown in Table 2. From these results it is clearly understood that the present steel sheet has an excellent formability in respect of deep drawing and stretching.

TABLE 1 Higher carboxylic acid base Metallic coating coating material and lubricant Amount Amount, Metal Plating method g./m. Material g./m.

0.2 10 0. 2g 6 i 0 a? #120 machine oil 3 Commercial press oil 6 10 0. 2 it? 0 2 10 {#120 machine oil. 1 0. 2 machine oil, 3 100 0. 2 #120 machlne o 0 g 56 #mdr'niiiiiii'il. 1; (2)1IIIIIIIIIII III 0.'25 }Nonplated #120 machine oil 3 V' Commercial press oil 6 *Inventive steel sheet.

Comparison steel sheet.

(1) Paimitic acid.

(2) A mixture of one part of palmitic acid and 0.25 part of di-eyclohexyl amine dissolved in toluene was applied and dried.

TABLE 2 Conical cup test Erichsen value value Inventive steel sheet. Comparison steel sheet.

EXAMPLE 2 1 g./m. of zinc coating was applied on a cold rolled rimmed steel sheet of 0.8 mm. thickness, and then palmitic acid dissolved in toluene was coated on the surface and dried. The amount of the palmitic acid coating was increased stepwise and press formability of the steel sheet was tested. The results are shown in Table 3.

TABLE 3 Maximum stretching Amount of Palmitine Conical cut height acid coating (mg/m!) value (mm) (mm.)

By a round-bottom pucnh. Blank dia: 50 mm. 2 By a flat-bottom punch of 40 mm. dia. Frange clamped.

From the results of this example it is seen that an excellent forming quality can be obtained when the amount of palmitic acid coating is not less than 10 mg./m. Similar results were obtained when other coating materials were used.

EXAMPLE 3 10 g./m. of zinc electroplating was applied on cold rolled, rimmed steel sheets of 0.8 mm. thickness, and then the following treatments were applied. Results of various tests are shown in Table 4. Testpieces A-K are present inventive steel sheets and L-P are comparison steel sheets.

Treatments Testpieces (inventive steel sheets):

A-Lauric acid as toluen solution was applied and dried (non-volatile matter: 200 mm./m.

B-Palmitic acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

CStearic acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

DBehenic acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

E-Sebacic acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

F-Beef tallow fatty acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

G-Palm oil fatty acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

HHardened castor oil fatty acid as toluen solution was applied and dried (non-volatile matter: 200 mg./m.

IHardened fish oil fatty acid as toluen solution was ap plied and dried (non-volatile matter: 200 mg./m.

J-Palmitic acid was melted by heating and applied (nonvolatile matter: 200 mg./rn.

KSolid palmitic acid was directly spread on the steel surface and melted by an infra-red lump (non-volatile matter: 200 mg./m.

Test pieces (comparison) LZinc electroplating was applied on one side and press oil (also for rust prevention was applied 3 g./m.

M-Only zinc electroplating on one side.

NSame treatment as A was applied on non-plated, cold rolled, rimmed steel sheet of 0.8 mm. thickness.

OSame treatment was C was applied on non-plated, cold rolled, rimmed steel sheet of 0.8 mm. thickness.

PNon-plated cold rolled, rimmed steel sheet of 0.8 mm.

was directly tested.

TABLE 4.FO RMABILITY Formability testing Conical cup test.-N0 lubricant was used. Same as in Example 2 except conical cup testing was made with the treated surface faced on a die side.

Punch stretching iest.-Measured with the treated surface faced on the punch side.

Treatment material removing test.-Aqueous solution of parkocleaner- N 358 (I0 g./l) was used. Those which show complete Wettability with water of the zinc based metallic coating or the naked steel sheet surface after spray washing with an aqueous soiutiion at 60 C. for 20 seconds are regarded as good.

EXAMPLE 4 Various zinc base metallic coatings were applied on cold rolled, rimmed steel sheets (A-J) of 0.8 mm. thickness, and a toluene solution of palmitic acid was coated on the one side of the steel sheets and dried to give 2 g./m. of non-volatile matter coating. Forming qualities of these steel sheets and the comparison steel sheets B and K were tested. The results are shown in Table 5.

Steel sheets A-Coated with hot dip zinc coating of g./m.

BC0ated with hot dip zinc coating of 100 g./m. and heat treated to alloy thezinc coating with part of the steel sheet substrate thus forming a zinc-iron alloy layer.

BCommercial press oil was applied on similar steel sheet as B (Comparison) CCoated with hot dip zinc-tin alloy (Sn: 25%) plating of 100 g./m.

DCoated with zinc electroplating of 50 g./m.

E-Coated with zinc electroplating of 10 g./m.

F-Coated with zinc electroplating of 2 g./m.

GCoated with zinc electroplating of 500 mg./m.

H-Coated with zinc electroplating of 250 mg./m.

I-Coated with zinc electroplating of 100 mg./m.

I-Coated with zinc electroplating of 10 mg./m.

K--Commcrcial press oil was applied on a non-plated steel sheet.

EXAMPLE 5 A number of test pieces similar to steel sheets A and B of Example 4 were made, and conical cup tests were done with the treated surfaces of the testpiece faced on the die side. As comparison, non-treated steel sheets A and B corresponding to steels A and B, were subjected to conical cup tests. Sheets A and B were lubricated with spindle oil on their die sides. The results are shown in FIG. 2, in which the average conical cup values of every five testpieces from the beginning of the test are plotted against the testing order.

On the other hand, the testpieces A and B were continuously subjected to Erichsen tests with the treated surface faced on the punch side, and as comparison, nontreated testpieces A' and B corresponding to the testpieces A and B were also tested with Vaseline lubricated on the punch side surface of the testpieces. Results are shown in FIG. 3, in which the ordinate shows an average value for every five testpieces.

The results indicates that the present steel sheet which are treated with palmitic acid are far more constant in their test values and do not give any elfect on the tool by repetition of tests, whereas the non-treated steel sheets which are lubricated with spindle oil or vaseline only show substantial variation in their measurements, which clearly indicates the eflect of burning of the metallic layer.

EXAMPLE 6 TABLE 6 Maximum Conical punch cup stretching value height (m (mm) Testpiece:

As seen from the above results, the chromate treatment does not hinger the lubricity of the present steel sheet.

10 EXAMPLE 7 Cold rolled, rimmed steel sheets of 0.8 mm. thickness were deep drawn into a square X 100 mm.) box using a square blank (220 X 220 mm.) under a blank holder pressure of about 10 tons. Steel sheets lubricated with machine oil or relatively low viscosity press oil were broken at a depth of 10 to 30 mm., while steel sheets applied with high viscosity press oil containing extreme-pressure additives and the present steel sheets which had been coated with 2 g./m. of zinc electroplating and applied with palmitic acid as toluene solution and dried to give about 300 mg./m. of non-volatile matter could be easily drawn without using other lubricant.

The maximum punch load in case of the present steel sheets was 520% lower that of the steel sheets which were applied with other oil lubricant.

EXAMPLE 8 Lead electroplated (plating thickness: 1 g./m. steel sheets of 0.8 mm. thickness were coated with various amounts of palmitic acid as toluene solution on the side and subjected to formability tests, the results of which are shown in Table 7.

TABLE 7 Conical cup 1 Erichsen value value 1 (mm (mm.

Amount of palmitic acid (mg/m9):

1 With the treated surface faced on the die side. 2 The treated surface faced on the punch side.

EXAMPLE 9 The following steel sheets A to I were subjected to various tests, the results of which are shown in Table 8. Steel sheets A to E are lead-tin alloy (Sn: 15 wt. percent) hot dip plated (plating thickness, 100 g./m. and are treated as under on one side, and there sheets fall within the scope of the present invention. Steel sheets F to J are set forth as comparison and include plated steel sheets with various treatments and non-plated steel sheets with various treatments.

Steel sheet: Treatment A-Coated with lauric acid as toluene solution and dried (non-volatile matter: 200 ing/m?) B--Coated with palmitic acid as toluene solution and dried (non-volatile matter: 200 mg./m.

CCoated with stearic acid as toluene solution and dried (non-volatile matter: 200 mg./m.

DCoated with molten palmitic acid (non-volatile matter: 200 mg./m.

E-Spread with solid palmitic acid, which was reflowed with an infra-red lamp (non-volatile matter: 200 mg./m.

F (comparison)Coated with rust preventing and lubricating oil in an amount of 3 g./m.

.G (comparison)Non-treated, plated steel sheet H (comparison)Naked steel sheet with same treatment as A I (comparison)Naked steel sheet with same treatment as F I (comparison)Naked steel sheet with no treatment TABLE 8 Erichsen value (1mm) Dry.

1 Comparison..

Forma-bility tests were done in similar way as in Example 3.

EXAMPLE 10 the die side. Results are shown in FIG. 4, in which the ordinate shows an average value for every five testpieces in series from the beginning of the test.

On the other hand testpieces B were continuously subjected to Erichsen tests with the treated surface faced on the punch side. As comparison, similar lead-tin alloy plated steel sheets B which were not surface treated were also tested with vaseline applied on the steel surface on the punch side. Results are shown in FIG. 5, in which the ordinate shows an average value for every five testpieces.

In all cases, the present steel sheets which were treated with palmitic acid showed far less variation in their measurements and did not affect the tools by repetition of tests, While in case of comparison steel sheets in which spindle oil or Vaseline was used remarkable variations in the meas urement were seen at the beginning, which clearly indicate the burning of metallic layer.

What is claimed is:

1. Surface treated steel sheet suitable for forming works which comprises metallic coating applied on a steel sheet surface, said metallic coating being composed of material selected from the group consisting of zinc, lead, zinc base alloy and lead base alloy, and a layer of higher carboxylic acid based material applied on the metallic coating, said higher carboxylic acid based material being solid at room temperatures.

2. Surface treated steel sheet according to claim 1 in which the higher carboxylic acid based material contains amine.

3. Surface treated steel sheet according to claim 1 in which the metallic coating is not less than 250 mg/m. in respect of zinc or lead content.

4. Surface treated steel sheet according to claim 1, the metallic coating is not less than 250 mg./m. in respect of zinc or lead content, and the layer of higher carboxylic acid based material is not more than 5 g./-m.

5. Surface treated steel sheet of claim 1 wherein the layer of higher carboxylic acid based material is not more than 5 g./m.

6. Surface treated steel sheet of claim 2 wherein the layer of higher carboxylic acid based material is not more than 5 g./m.

7. Surface treated steel sheet according to claim 1, wherein a thin layer of hydrated chromium oxide and/ or silicon oxide is interposed between said metallic coating and said layer of higher carboxylic acid based material.

References Cited UNITED STATES PATENTS L. DEWAYNE RATLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner U.S. Cl. X.R. 72-42 

